The invention concerns an internal combustion engine, especially an Otto engine, with a fuel injector.
Gasoline engines with direct injection of the fuel into the combustion chamber, i.e., not into the intake port, suffer especially from the problem of the formation of carbon deposits on components. Carbon deposits form especially in the neck region of intake valves. A more exact analysis of how these carbon deposits form leads to the following result: Oil and fuel constituents first form a sticky coating on the components. These constituents are chiefly long-chain and branched-chain hydrocarbons, i.e., the low-volatility components of oil and fuel. Aromatic compounds adhere especially well. This sticky base coating serves as a base for the deposition of soot particles. This results in a porous surface, in which oil and fuel particles in turn become embedded. This process is a circular process, by which the coating thickness of the carbon deposits continuously increases. Especially in the area of the intake valves, the deposits originate from blowby gases and from internal and external exhaust gas recirculation, and in this process, the blowby gases and the recirculated exhaust gas come into direct contact with the intake valve.
Especially in the area of the neck of the intake valves, excessive carbon deposits have extremely negative effects for the following reasons: In the case of Otto direct injectors, the successful ignition of the stratified charge depends to a great extent on correct development of the internal cylinder flow, which ensures reliable transport of the injected fuel to the spark plug to guarantee reliable ignition at the spark plug. However, a coating of carbon deposits in the neck region of the intake valve may interfere so strongly with the tumble flow that ignition failures may occur there as a result. Under certain circumstances, however, ignition failures can lead to irreversible damage of a catalytic converter installed in the exhaust gas tract for purifying the exhaust gas. Furthermore, the coating of carbon deposits in the neck region of the intake valve causes flow resistance, which can lead to significant performance losses due to insufficient cylinder filling, especially in the upper load and speed range of the internal combustion engine. In addition, the carbon deposits in the neck region of the intake valve may prevent correct valve closing, which leads to compression losses and thus sporadic ignition failures. This in turn could irreversibly damage the catalytic converter. There is the potential for small particles to break away from the coating of carbon deposits in the neck region of the intake valve and get into the catalytic converter. These hot particles may then cause secondary reactions and corresponding local damage of the catalytic converter. For example, a hole may be burned in the structure of the catalytic converter.
Globular deposits are found especially on the valve stem downstream from a partition plate in the intake port. Due to the dripping of high-boiling hydrocarbons from the partition plate towards the valve neck or valve stem, globular carbon deposits eventually form there by the sequence of events explained above. These deposits on the valve stem can result in flow deficits due to undesired swirling and turbulent flow around the globular carbon deposits. This may persistently interfere with the formation of stable tumble flow from cycle to cycle.
A possible solution would be to keep these sources of deposits away, for example, from the intake valve, by completely eliminating exhaust gas recirculation and the introduction of blowby gases into the intake port. However, with the combustion behavior of modern reciprocating internal combustion engines, at least external exhaust gas recirculation and the introduction of blowby gases into the intake port are absolutely necessary for reasons of emission control and fuel consumption, so that this approach is not possible.
U.S. Pat. No. 4,809,662 describes the controlling of spark advance to increase combustion chamber temperatures so as to clean off the deposits.
EP 0 785 350 A2 describes a cooling measure for a discharge orifice of a fuel injector to prevent deposits on the injection orifice. Similarly, it is known from DE 197 47 268 A1 that a nozzle body of the injection nozzle can be cooled by injecting supplementary liquid so as to counteract carbon deposits in the nozzle bore.
EP 0 798 560 A1 describes keeping some fuel on a nozzle holder surface to prevent deposits on the injection nozzle.
DE 197 56 119 A1 deals with a means of preventing carbon deposits on the spark plug. To this end, a control unit is used to terminate the injection of fuel before the fuel is ignited. This is intended to prevent carbon deposits from forming on the spark plug, especially during starting of the internal combustion engine. DE 199 11 023 A1 describes a method for preventing the formation of carbon deposits on the spark plug, by injecting the fuel in a conical spray to avoid wetting the spark plug with fuel. U.S. Pat. No. 5,913,302 describes a cleaning strategy for a spark plug in an internal combustion engine with a two-stroke cycle. To this end, the ignition coil dwell time is raised for a short period of time to clean carbon deposits on the spark plug.
U.S. Pat. No. 4,703,734 describes valve overlapping and sequential opening of intake valves for operation at low speeds and for operation at high speeds to prevent the formation of carbon deposits.
DE 31 33 223 A1 describes an internal combustion engine, in which combustion chamber and intake manifold walls that come into contact with the fuel-air mixture to be ignited or with combustion gases are coated with a material of a type such that the temperatures that develop on these coated walls during operation of the internal combustion engine are high enough to prevent the formation of deposits. At the same time, however, the heat capacity is kept sufficiently low that the coated walls do not significantly increase the temperatures of fuel-air mixtures entering during the intake and compression cycles.
EP 00 48 333 A1 provides an intake valve with a shield in the region of the valve neck to counteract the formation of carbon deposits by lowering the surface temperature.
DE 199 45 813 A1 describes a method of operating an internal combustion engine, in which systematic measures for cleaning the combustion chamber are initiated when deposits are detected in the combustion chamber. For example, knocking combustion is induced and/or a cleaning liquid is added to the combustion air intake.